user
Write an algorithm to identify prime numbers.


assistant
def is_prime(n):
  if n <= 1:
    return False
  if n <= 3:  
    return True  
  if n % 2 == 0 or n % 3 == 0: 
    return False  
  i = 5
  while i*i <= n:
    if n % i == 0 or n % (i + 2) == 0: 
      return False
    i = i + 6
  return True